Research On Permanent Magnet Direct-drive Wind Power System Grid-connected Frequency Dynamic Response And Harmonic Suppression Technology

Wind power is one of the main forms of renewable energy power generation.Wind power installed capacity in the grid continues to increase.Wind power high penetration rate is an inevitable trend of the future grid.In the process of wind power technology research and application,it is a hot spot to address poor dynamic response and harmonic suppression ability problem for grid-connected traditional wind power systems.In order to improve the friendly grid connection capability of the permanent magnet direct drive wind power system,this dissertation conducts research on wind power stability key issues and technologies,such as the dynamic response and harmonic suppression at grid-connected point.The mechanism of the key issues is revealed in theory.The ways and measures for key issues are sought.These ways and measures establish the foundation for engineering applications.Firstly,the architecture,transient power flow and mathematical model of permanent magnet direct drive wind power system are studied.From system architecture,the transient power flow participating in dynamic response is analyzed.This transient power is provided by DC side super capacitor energy storage,and its mechanism is clarified.The transient power flow establish a foundation for the virtual inertial and damping method research.Considering the virtual current and voltage source power generation mode,the dynamic mathematical model of the system is established.This dynamic mathematical model achieves wind power system operation and simulation under the two modes.A system seque nce impedance model based on LCL filter network is proposed to adjust dynamic model parameters.The adjustment guarantees the impedance analysis accuracy of dynamic model.Secondly,in order to address the weak dynamic response ability issue of wind power system,the grid state parameter detection and virtual inertia and damping control strategy are studied.The influence of complex grid on the amplitude and frequency detection results of the delay signal cancellation enhanced phase-locked loop(DSC-EPLL)is analyzed.A delay signal cancellation and moving average filter enhanced phase-locked loop(DSC-MAF-EPLL)is proposed.The DSC-MAF-EPLL realizes the accurate state parameter detection under complex power grids,such as frequency.The virtual inertia and damping controls based on supercapacitor energy storage are proposed.These methods improve the system ability of grid dynamic response,thus the grid frequency fluctuation is suppressed effectively,and this method establishs the foundation for harmonic suppression.Thirdly,in order to address the output harmonic suppression issue under the current source mode,the resonance damping and low-frequency harmonic suppression methods are studied for the grid-connected interface.The influence of weak grid on capacitive current feedback active damping method is analyzed.A wide positive damping interval multi-state feedback active damping method is proposed.This method has better stability and effectively suppresses port network resonance under weak grid.The system output impedance of the quasi-proportional resonant control is analyzed under the current source mode.The harmonic impedance compensation method of the proportional odd-order multi-resonant repetitive control is proposed.The low-frequency current harmonics are suppressed rapidly and effectively by this method under the harmonic grid.Finally,in order to solve the output low frequency harmonic suppression issue under the voltage source mode,the harmonic suppression method under the local strong nonlinear load is studied for the grid-connected interface.The limitation of proportional odd-order multi-resonant repetitive control is analyzed.A specific harmonic gain compensation method is proposed to achieve effective suppression of the 5th and 7th harmonics.The influence of low sampling frequency on the phase compensator is analyzed.A simple fractional-order phase compensation method is proposed to achieve effective harmonic suppression under low sampling frequency.Based on the proposed method and key technology,simulation and physical simulation experiments are carried out for analysis and comparison verification.These results verify the correctness of the proposed methods and theoretical analysis.